1. Field of the Invention
The present invention relates to a print head of an ink-jet printer, which has resistance against corrosion by ink, thus, reliability is improved, and a method of manufacturing the print head.
2. Description of the Related Art
One of well known printers is an ink-jet printer. The ink-jet printer has a print head in which multiple nozzles for outputting ink droplets to a recording sheet of paper or textile are disposed, thus, images and characters are printed thereon. The ink-jet printer has several merits, for example, quiet operation, no fixing treatment, and easy full-color printing.
There are some methods for outputting the ink droplets. Typical ones are piezoelectric ink-jet, thermal ink-jet, and the like.
The piezoelectric ink-jet printer uses electromechanical transducers such as piezoelectric elements which mechanically deform ink chambers to produce alteration in ink pressure. The pressure alteration causes output of ink droplets through minute nozzles.
The thermal ink-jet printer employs minute heating elements in firing chambers. The heating elements forms bubbles of vapor in the ink in very short periods when electric current applied to the heating elements. Expansion of the bubble pushes out an ink droplet through a nozzle. The thermal ink-jet print head is categorized into two types, side shooter and roof shooter. In the side shooter type head, a bubble generated by a heating element expands and pushes ink in the direction parallel to the heating element surface to output an ink droplet through a nozzle which is placed away from the heating element. On the contrary, the roof shooter type head features that nozzles are formed just above heating elements. A bubble generated by the heating element pushes out ink in the vertical direction to output an ink droplet through the nozzle. It has been known that required power consumption of the roof shooter type head is less than that of the side shooter type head.
A roof shooter type head comprises multiple (for example, 64, 128, or 256) heating elements, drive circuits which drive the heating elements individually, ink passages, and nozzles. During manufacturing process, the roof shooter type heads formed on a silicon wafer having diameter of equal to or larger than 6 inch (approx. 15.24 cm). The wafer has 90 or more blocks (approx. 10xc3x9715 mm each), and the heads are formed at once so that one head is formed in one block. At that time, silicon LSI formation technique or thin film formation technique is used to form the print heads to have monolithic structure.
FIG. 1A is a plan view showing an ink output surface of a roof shooter type print head 1 for an ink-jet printer (hereinafter, referred to simply as print head 1). FIG. 1B is an enlarged diagram showing an area indicated by a broken-line square xe2x80x9caxe2x80x9d in FIG. 1A. FIG. 1C is a cross sectional view along a line C-Cxe2x80x2 in FIG. 1B. In FIG. 1B, components under an orifice plate 14 are shown through it.
Drive circuits (not shown) are formed on a chip substrate 2 by LSI formation technique. A common ink supply groove (not shown) is formed on the chip substrate 2 by etching or the like. An insulation layer 3 (oxidized film) is formed on the chip substrate 2 on which the drive circuits and the common ink supply groove have been formed.
Plural lines (64, 128, or 256 lines) of heating resistor 4 is formed with thin film formation technique such as photolithography, between the drive circuits and the common ink supply groove. Further, common electrodes 6 and individual electrodes 7 for driving heating areas 5 on the heating resistor 4 are formed so that the heating area 5 of the heating resistor 4 are exposed. A set of one heating area 5, one common electrode 6, and one individual electrode 7 is a unit of one heating element.
The individual electrodes 7 are connected to electrode terminals of the drive circuits. A connection terminal 8 for connecting the common electrodes 6 to peripherals and another set of connection terminals 9 for connecting the drive circuits to peripherals are formed on the chip substrate 2.
A wall material layer is deposited onto the chip substrate 2 except the portion where the connection terminals 8 and 9 are formed. Then photolithography is performed to pattern the wall material layer, thus a wall 11 is formed. The wall 11 determines an ink flow passage 13.
The wall 11 includes comb like extensions 11-1. The wall 11 and its extensions 11-1 surrounds three sides of each heating area 5 to separate them from each other. Separated spaces above the heating areas 5 are firing chambers 12. Open side of each firing chamber 12 is connected to an ink flow passage 13 which is communicated with the common ink supply groove.
An orifice plate 14 is deposited onto the wall 11. Multiple nozzles 15 are formed in the orifice plate 14 so that a set of the nozzles 15 forms a nozzle line 16 being along a line of the heating areas 5. Thus, multiple print heads 1 are formed on the silicon wafer. The silicon wafer is finally diced so that chip substrates 2 each having the formed print head 1 thereon are separated from each other.
In the printer, ink is supplied to the firing chambers 12 via the common ink supply groove and the ink flow passage 13. For printing, electric current is selectively applied to the heating areas 5 in accordance with print data. Upon reception of the electric current, the heating area 5 heats ink for a very short time period, thus a bubble of vapor is generated at bottom of the ink layer. The bubble expands and pushes out an ink droplet through the ink nozzle 15 above the heating area 5. Size of the ink droplet is almost the same as that of the nozzle diameter when output. When the droplet reaches a sheet, it is broadened almost twice as large as the initial size.
Aluminum (Al) is a major material for electrodes such as the common electrode 6 and the individual electrode 7 because good conductivity is available with low cost. Since aluminum is amphoteric metal, it will be corroded gradually under ordinary acid or alkaline ink.
Gold (Au) is one of corrosion resistant material, therefore, it is suitable one for the common electrodes 6 and the individual electrodes 7. However, Au is likely to cause migration which diffuses ink into boundary between electrodes 617 and the heating resistor 4. This ink migration will separate the Au electrode from the heating resistor 4 eventually.
Such the corrosion of the electrodes 6 and 7 or separation of the electrodes from the heating resistor 4 will deteriorate print head performance, and the print head 1 will be broken eventually. Even if the electrodes 6 and 7 are not corroded by ink, humidity in the air causes the migration, therefore, the print head disorder may be prolonged but it will be also broken eventually.
It is an object of the present invention to provide an ink-jet printer head having resistance against corrosion and migration caused by ink, thus reliability is improved. It is another object of the present invention to provide a method for easy manufacture of a print head for an ink-jet printer having resistance against corrosion and migration caused by ink, thus reliability is improved.
An ink-jet printer head according to a first aspect of the present invention is an ink-jet printer head in which ink is pressed out in predetermined directions by vapor bubbles generated by heating the ink, the ink-jet printer head comprises:
an insulation substrate at least a surface thereof is an insulator;
a plurality of heating resistors which are formed on the insulation substrate, each of which has a heating area which emits heat when a predetermined voltage is applied thereto;
a pair of electrodes which is electrically connected to each of the heating areas;
a wall which is formed on the insulation substrate to determine an ink flow passage; and
a barrier layer, having resistance against corrosion caused by the ink, which covers the electrodes so that the electrodes are not exposed to ink in the ink flow passage.
According to this invention, electrode corrosion caused by ink and migration are prevented. Thus, the ink-jet printer head has improved resistance against corrosion and migration caused by the ink. As a result, reliability of the ink-jet printer head improves.
The barrier layer may be made of amorphous metal alloy.
The barrier layer may be made by electroless plating. The electroless plating realizes uniform and constant barrier layer which firmly adheres to the electrodes.
The electrodes may be superimposed on the heating resistors except the heating areas. In this case, a contact layer which interconnects the electrodes and the heating resistors should be formed between the electrodes and the heating resistors. And the barrier layer may cover top surfaces and edges of the electrodes so that the electrodes are not exposed to the ink in the ink flow passage.
The heating areas may be uncovered by the barrier layer to be exposed.
The barrier layer, however, should be formed on each of the electrodes and predetermined regions on the heating areas. This structure successfully prevents migration at contact surfaces between the electrodes and the heating resistors.
A protective insulation film may be formed over the heating areas and the barrier layer. In this case, heating resistors may be made of Taxe2x80x94Sixe2x80x94Oxe2x80x94N, the barrier layer may be made of Tixe2x80x94W, and the protective insulation film may be made of Taxe2x80x94Sixe2x80x94O. This structure prevents a short circuit current from flowing through the ink in case of a monolithic ink-jet printer head. As a result, smooth ink flow is realized and reliability of the ink-jet printer head improves.
An ink-jet printer head according to a second aspect of the present invention is an ink-jet printer head in which ink is pressed out through nozzles in predetermined directions by providing pressure to the ink, the ink-jet printer head comprises:
pressure generators, disposed within an ink flow passage communicating to the nozzles, which provide the ink with pressure when a predetermined voltage is applied thereto;
electrodes which are terminals for providing the pressure generators with the predetermined voltage; and
a barrier layer, having resistance against corrosion caused by the ink, which covers the electrodes so that the electrodes are not exposed to the ink in the ink flow passage.
This structure also realizes a reliable ink-jet printer head which has excellent resistance against corrosion and migration caused by ink.
A manufacturing method of an ink-jet printer head according to a third aspect of the present invention is a manufacturing method of an ink-jet printer head in which ink is pressed out in predetermined directions by vapor bubbles generated by heating the ink flowing in an ink flow passage, the method comprises:
forming a plurality of heating elements by forming heating resistors, each having a heating area which emits heat when a predetermined voltage is applied thereto, on an insulation substrate and forming pairs of electrodes on the heating resistors except the heating areas;
forming a barrier layer, having resistance against corrosion caused by the ink, which covers the electrodes so that said electrodes are not exposed to the ink in the ink flow passage.
According to the above invention, a reliable ink-jet printer head having excellent resistance against corrosion caused by ink is manufactured with easy process.
The forming barrier layer may comprise forming the barrier layer of amorphous metal alloy.
The forming barrier layer may comprise forming the barrier layer by plating. In this case, it is preferable that the barrier layer comprises forming the barrier layer by electroless plating. This method realizes a uniform and constant barrier layer which successfully protect the electrodes from ink.
The forming barrier layer comprises forming the barrier layer by photolithography. According to this method, corrosion at contact surfaces between the electrodes and the heating resistors, that is, the migration, is prevented effectively.